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(11) | EP 0 234 924 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Hydrocarbon treatment process |
| (57) A process wherein lower boiling products (H) are obtained from a hydrocarbon feed
(J and/or HH) by contacting the feed with fluidized solid contact material at elevated
temperature in a riser (K), spent contact material is separated and stripped of volatile
hydrocarbons in a stripping zone (D), stripped contact material is regenerated with
oxygen-containing gas (A) in a regeneration zone (B), and hot freshly regenerated
fluidized solid contact material is returned to the riser (K), the process further
including two or more of the following:
(i) suspending hot regenerated contact material in a carbonizable lift gas at the lower portion of the riser and injecting hydrocarbon feed higher in the riser; (ii) charging hydrocarbon feed into the base of the riser, steam cooling a portion of the hot freshly regenerated contact material, and contacting the hydrocarbon feed with hot regenerated contact material upstream of where said hydrocarbon feed is contacted with the steam cooled contact material; (iii) cooling a portion of hot freshly regenerated contact material before returning it to the riser; and (iv) adding a portion of freshly heated regenerated contact material to said stripping zone. |
[0001] This invention relates to a process and system for obtaining light fractions from heavy hydrocarbon oils, including processes for selective vaporisation and processes for converting heavy hydrocarbons containing high concentrations of coke precursors and heavy metals into gasoline and other liquid hydrocarbons. In a preferred embodiment this invention is directed towards the fluid catalytic cracking of hydrocarbons to obtain products boiling in the motor fuel range.
[0002] The fluid catalytic cracking process, with the advent of the highly active zeolitic type catalysts, has evolved into the generally standardized practice of effecting essentially cocurrent ascending flow of hydrocarbon vapors and the finely divided catalyst in an elongated tubular reaction zone referred to in the industry as a riser. Notwithstanding the brevity of the reaction cycle, which is usually in the order of about 10 seconds or less, there is a laying down of coke on the catalyst thereby adversely affecting its activity as well as undesirably altering product yield distribution upon reuse. Accordingly, it is the universally observed procedure to separate the catalyst from the riser effluent and recycle it to the process via a regenerator which serves the dual purpose of combusting the coke contaminants and heating the catalyst for reuse in the reaction cycle.
[0003] In accordance with the prior art, separation of the catalyst from the cracked hydrocarbons is carried out within a so-called disengaging chamber which contains a stripping zone. The disengaging chamber is a contained vessel either forming a relatively voluminous shroud about the downstream extremity portion of the riser or externally positioned and axially aligned therewith. In the latter type arrangement, the fluid stream of catalyst and converted hydrocarbons is discharged into the disengaging chamber directly from the riser via a sidewise opening or port. In said shroud-type arrangement, however, it is generally preferred to pass the riser effluent from said sidewise opening or port firstly through a singlestage cyclone vented to the disengaging chamber. Due to the substantial reduction of the superficial space velocity experienced in the disengaging chamber in either of said modes of operation, a considerable portion of catalyst entrained in the riser effluent settles out and collects at the bottom of the chamber. The gas stream along with the stripping vapor thereupon is vented to the fractionator from disengaging chamber via a cyclonic separator positioned therein serving to collect predominantly all of the entrained catalyst.
[0004] In light of the fact that the modern zeolitic cracking catalysts range in particle size from about 5 to 100 microns with the major portions thereof being in the order of from about 40 to 80 microns, separation thereof as practiced in accordance with the aforesaid prior art is nonetheless remarkably efficient. However, the relatively small amount of catalyst entrained in the cracked stream poses a problem because of the tremendous cumulative throughput thereof. In some cases, the foremost problem is that the entrained catalyst leaving with the cracked stream must be recycled thereto in the form of a slurry oil recovered from the fractionator thereby reducing the amount of feedstock that can be accommodated in the cracking unit. Thus, optimal processing efficiency of the cracker is sacrificed.
[0005] Additionally, there has always been a need in the prior art to affect rapid disengagement of the catalyst from reaction products in order to mininize undesirable reactions which can take place thereby detracting from the overall efficiency of the process when considered as a whole.
[0006] As can well be appreciated by those skilled in the art, a necessary and integral part of a fluid catalytic cracking reactor involves the regenerator wherein the spent catalyst has its activity restored. Regeneration of spent catalyst is generally effected after separation of the spent catalyst from the reaction products. The spent catalyst is removed from the reaction zone and contacted in a stripping zone with a stripping medium, usually stean, to remove vaporized and entrained and/or occluded hydrocarbons from the catalyst. From the stripping zone, a stripped catalyst is passed into a regeneration zone wherein the stripped spent catalyst is regenerated by burning coke deposits therefrom with an oxygen-containing gas, usually air. The resulting hot regenerated catalyst from the regeneration zone is then recycled to the reaction zone and contacted with additional hydrocarbon feed. The efficiency of stripping affects the heat released in the regenerator. In practice, commercial strippers are not completely efficient and residual hydrocarbon is present in the. catalyst discharged therefrom. Regenerator temperatures increase as the efficiency of stripping decreases.
[0007] The ratio of recycled regenerated catalyst to hydrocarbon feed, referred to generally as the C/O (cat-to-oil) ratio, affects selectivity in a typical FCC unit. The effect is most pronounced in a heavy oil FCC unit. The higher the C/O, the better the selectivity and the lower the contact time can be. Lower contact tine results in lower hydrogen transfer when using zeolitic cracking catalyst. Lower hydrogen transfer also results in higher gasoline octane, increased olefins for alkylation feedstock, and higher hydrogen content LCO for distillate production for a given conversion. In commercial FCC units, catalyst circulation rate (CCR) and catalyst to oil ratio (C/O) are not independent variables that can be changed at will. Heat balance considerations in commercial unit establish the operating C/0. Generally, the only variables that are Independently controlled is cracking temperature (in particular, the temperature at the outlet of the riser cracker) and feed preheat temperature.
[0008] Selective vaporization is carried out in equipment similar to that used in FCC operations. The fluid solid contact material, however, is substantially inert as a cracking catalyst. Selective vaporization occurs in a riser, called a contactor, and combustion of carbonaceous deposit takes place in a burner. See, for example, U. S. 4,263,128 (Bartholic) which is herein incorporated by reference. The technology is known in the industry as the ART process.
[0009] The term delta (Δ) coke is the weight percent of coke on spent catalyst minus the weight percent coke on regenerated catalyst. In other words,Δ coke is the weight of coke on spent catalyst minus the weight coke on regenerated catalyst divided by catalyst circulation rate (CCR). Delta coke is related to C/0 by the equation:
[0010] The present invention provides a process wherein lower boiling products are obtained from a hydrocarbon feed by contacting the feed with fluidized solid contact material at elevated temperature in a riser, spent contact material is separated and stripped-of volatile hydrocarbons in a stripping zone, stripped contact material is regenerated with oxygen-containing gas in a regeneration zone, and hot freshly regenerated fluidized solid contact material is returned to the riser, the process further including at least one, and preferably at least two, of the following :
(i) suspending hot regenerated contact material in a carbonizable lift gas at the lower portion of the riser and injecting hydrocarbon feed higher in the riser;
(ii) charging hydrocarbon feed into the base of the riser, steam cooling a portion of the hot freshly regenerated contact material, and contacting the hydrocarbon feed with hot regenerated contact material upsteam of where said hydrocarbon feed is contacted with the steam cooled contact material;
(iii) cooling a portion of hot freshly regenerated contact material before returning it to the riser; and
(iv) adding a portion of freshly heated regenerated contact material to said stripping zone.
[0011] The process of the invention provides means to operate a heat balanced FCC unit or a selective vaporization unit at an increased C/0 ratio. These means may be used alone or in combinations.
[0012] In accordance with one aspect of the invention, the CCR of an FCC unit, heavy oil FCC unit or selective vaporization process is controlled (increased) by directly cooling hot circulating fluid solid contact material. Preferably, hydrocarbon charge is fed directly to the base of a riser along with lift gas and/or steam, if needed, and contacted with hot regenerated fluid solid contact material upstream of the point at which the gasiforn mixture is contacted with cooled fluid solid contact material for increased C/0 in a heat balanced operation without cooling of the regenerator/burner system. This method of operation reduces thermal reactions and increases desired catalytic reactions in FCC units. This metnod of operation is also beneficial when feeds containing asphaltenes, basic nitrogen and metals, are being processed in FCC or selective vaporization units. By the method, feed is preheated with a minimun of hot regenerated material to remove the aforementioned impurities and the cooled solid contact material injected immediately downstream of the hot solid contact material injection maintains a high selectivity because active sites on the contact material are not covered with asphaltene (coke) deposits nor are they neutralized by basic nitrogen. Also, freshly deposited metals which are especially detrimental to activity have previously been removed during contact with hot regenerated contact material.
[0013] In another aspect, the invention comprises a system for controlling the operation of an FCC unit, heavy oil FCC unit or a selective vaporization process to increase C/0 and superheat reactor/contactor vapors by combining hot regenerated material with spent contact material directly into the spent contact material stripper, or in case of the apparatus, described hereinafter, by combining hot regenerated material with reactor/contactor products between the preseparator outlet and the high efficiency cyclone inlet and returning the hot regenerated material to the stripper through the high efficiency cyclone dipleg. This will lower the Δ coke on the circulating material which, in turn, will increase C/0 ratio by lowering the regenerator temperature. This results in lower carbon on spent material by vaporizing more of the hydrocarbon from the spent material in the stripper. A secondary beneficial effect is that the hydrocarbon vapors in the stripper and the high efficiency cyclone inlet are heated to a higher temperature than they would normally be heated. Since these vapors may be at their dew point, any cooling will normally result in condensation of the heavy ends, causing undesirable coke formation in the vessel, cyclones and vapor lines. By reheating these vapors, coke formation resulting from condensation reactions is reduced.
[0014] In still another aspect of the invention C/0 is increased in an FCC unit or heavy oil FCC unit operating with a zeolitic cracking catalyst by lifting regenerated catalyst with a lift gas that is capable of being cracked in a riser before regenerated catalyst contacts feed which is injected downstrean in the riser to control contact time. The lift gas that is used forms coke on the acid sites of catalyst before feed addition. As a result, the acid sites of the catalyst are deactivated by carbon formed when hot catalyst contacts lift gas. Preferred lift gases are either wet gas from the main column overhead receiver or any gas after recovery of C3' s and C4's in a gas concentration unit. The zeolitic sites are not deactivated and are available to crack a gas oil feed. Coke is reduced and yield structure is improved. This results in increased octane and olefin production, as well as higher C/0.
[0015] In an especially preferred embodiment, the process of this invention also employs controls on both the reactor (contactor) and the regenerator (combustor) so that there is complete control of the circulating solid material. In the first place, when the circulating material is in contact with combustion products (regenerator/combustor) or hydrocarbon vapors (reactor/contactor) it is in a dilute phase. After separation of the circulating material from the vapors or combustion products, the material is returned to a different vessel. The vast majority of other technology employed has a dense bed in contact with products of combustion or hydrocarbon vapors and utilizes cyclones to return the circulating material to the same vessel from which it came. This vessel always contains a dense bed of circulating material. In the novel process of this invention, the dilute phase system is connected directly to a preseparator and then to high efficiency cyclones such as multicyclones so that the circulating material is always discharged into another vessel separate from the vapors. This circulating material forms a dense bed in the secondary vessel, the secondary vessel being neither the reactor/contactor or the regenerator. The process is characterized by being a completely balanced system in that the separation efficiency is the same for both the reactor/contactor and the regenerator/combustor so that the two systems will retain the same particle size range. In the process, all the contact material entering the reactor/contactor and regenerator/combustor is maintained in a dilute phase and passes through the preseparator, i. e., there is no dense fluid bed in either the reactor/contactor or regenerator/conbustor. The novel process provides flexibility with respect to hydrocarbon feedstock composition, product distribution throughput and capacity. The process also results in more fines retention which will result in lower average particle size, more surface area, higher activity maintenance, and better. fluidization properties.
[0016] Further features and advantages of the process of this invention would be apparent from a detailed description of the preferred embodiment of the process as applied to the catalytic cracking of hydrocarbons.
[0017] The sole accompanying figure is a diagrammatic representation of a preferred form of apparatus of the present invention which is suitable for carrying out the process of this invention.
[0018] With reference to the figure illustrating a preferred embodiment of the catalytic cracking system of this invention, the system comprises a fast fluid type system that essentially operates in the dilute phase with all of the material transported from the bottom of the regenerator (B) to the top. The difference in this system when compared with conventional systems is (1) complete control of all catalyst flow into the system and (2) all the catalyst that flows into the system is transported by the air and eventually by the products of combustion through the regenerator to the cyclones (E) and (F). In this way, control is had not only of the total flow rate of air and combustion products but also the catalyst loading to the cyclone systems (E) and (F). The control of the catalyst allows control of pounds per cubic foot of catalyst entering the cyclones (E) and (F) and therefore gives control of the loading to the cyclone so that the system is not overloaded. Thus, air from a blower enters through line (A) and through the bottom of regenerator (B) containing catalyst to be regenerated and the flow rate is controlled to maintain a dilute phase. The catalyst and vapors are rapidly separated in preseparator (E) at a efficiency greater than 80% and the catalyst material passes through the bottom of preseparator (E) through line (R) into the regenerator surge hopper (C). Vapor materials exit (E) and pass into multicyclones (F) wherein flue gas is removed through line (G) and catalyst again passes through line (R) into regenerator surge hopper (C). The regenerator system is obviously built to burn off all the carbon from the spent catalyst. Therefore, this system is designed for certain temperature, pressure, and flow rate so that one can obtain the carbon burning in the desired time. The products of combustion from the regenerator that exit through flue gas line (G) are mainly nitrogen, C02, with a small amount of CO, i.e., less than 500 parts per million normally, SOx which is dependent on the amount of sulfur in the feed, water vapor contained in the combustion air and water vapor produced by combustion reaction. There is a small amount of NOx produced that is strictly based on the temperature of operation of the regenerator (B). Most of the nitrogen in the coke that is related to the nitrogen in the feed is liberated either as ammonia or as nitrogen. This system can also be operated to leave carbon on the regenerated catalyst by limiting the air to the regenerator. This may result in higher CO levels in the flue gas. The amount of CO will depend on the regenerator temperature, carbon level on regenerated material and oxygen supplied for combustion.
[0019] Since the spent catalyst is relatively cool, i.e., between 800°F. and 1100*F., the burning of carbon from this material is difficult at the time frame usually employed for the dilute phase burning in the regenerator, i.e., 3 to 15 seconds. For this reason, a hot recirculation valve (0) is provided that circulates back hot material from the regenerator surge hopper (C) back to the base of regenerator (B). The purpose of this line is to control the temperature in regenerator (B) so that the carbon or coke can be burned off the spent catalyst in the time allowed in the dilute phase transport riser regenerator. Typically, the ratio of the circulation rate through valve .(0) and the circulation rate through spent slide valve (JJ) is at least 1:1 and in many cases will be 2:1 or greater so that the temperature in this system can be raised to that in which burning can take place completely to C02 and all the carbon burned off the catalyst. The figure also includes a preferred, though not an essential, embodiment of the novel process of the invention, namely catalyst cooler (N) whose flow rate is controlled by slide valve (P). This valve is used when the regenerator temperature reaches its maximum metallurgical limits in order to protect the equipment against excessive damages or to obtain a maximum temperature based on catalyst activity maintenance or C/0 consideration. In other words, if it is desired to operate the regenerator at a temperature of about 1600°F., when the temperature in the system approaches that temperature the flow would be started through slide valve (P) which would move more material from regenerator surge hopper (C) through the catalyst cooler (N) and through the valve (P). As is obvious, this works opposite of valve (0) in that it would be removing heat by generating stean in the catalyst cooler (N) and therefore lower the overall systen temperature in the regenerator.
[0020] As can well be appreciated, both control valves (P) and (0) can be used. If one wishes to produce steam in order to supply energy to a refinery, valve (P) can .be used continually in the open mode to generate a constant amount of stesn. There may also be reasons to operate at cooler temperatures in the regenerator because catalyst activity maintenance, catalyst to oil relationships in the reactor or contactor (K), or due to the desired reaction kinetica. As indicated earlier, at the top of transport riser regenerator (B) all of the catalyst and air used for combustion enters preseparator (E). Preseparator (E) is designed so that the mininun efficiency must be greater than 80% and preferably greater than 90% removal of the solids from the gas. The solids removed are discharged from separator (E) through regenerated solids line (R) to the regenerator surge hopper (C). This return of the material from the preseparator (E) to the surge hopper (C) is done at a level lower than the bed level in surge hopper (C) so that the pipe is submerged in an actual level to prevent back flow of gas up the pipe into preseparator (E) causing preseparator (E) to natlfunction. The flue gas that exits preseparator (E) has only 20% or less of the catalyst with which it came into preseparator (E) and it flows out to the high efficiency cyclone system (F) for final clean up. The total clean up in this system is greater than 99.0%, and preferably greater than 99.99%, and the essentially catalyst-free gas exits high efficiency cyclone (F) through line (G) to flue gas treating and/or the atmosphere. The catalyst that is separated in high efficiency cyclone (F) is returned to the regenerator surge hopper (C) again below the normal level of catalyst so that this dipleg is sealed.
[0021] The regenerator surge hopper (C) is fluidized by controlling a small amount of air from the air blower into the system through an air distributor so that the material is naintained at at least the velocity of about one-half foot a second but no greater than 3.3 ft. a second in the vessel. The gas carrying some catalyst exits through regenerator hopper (C) through line (L) which is connected back to the regenerator (B). Line (L), the surge hopper vent, is also an equalizing line and is a very key feature of this process. This line assures that the pressure at the inlet to preseparator (E) and the pressure on surge hopper (C) are equal so at no time can surge hopper (C) be at a much higher pressure than preseparator (E). If the surge hopper (C) were at a higher pressure than preseparator (E) then it would be possible that the naterial that was separated in preseparator (E) could not flow down pipe (R) into the surge hopper and therefore cause preseparator (E) not to function. The sane pressure differential or equalization is necessary from high efficiency cyclone (F) to surge hopper (C). Surge hopper (C) can be at a slightly higher pressure than either (E) or (F) as long as the level in the return pipes (R) is not high enough to cause preseparator (E) and high efficiency cyclone (F) to malfunction. The vent line (L) is shown connected to the dilute phase regenerator (B). However, the vent line (L) from the regenerator inventory surge hopper (C) could also be placed between (E) and (F) and that choice depends on the velocity component in regenerator surge hopper (C). In any event, the purpose of vent line (L) is to insure that the pressure at inlet to presepartor (E) and the pressure on surge hopper (C) are equal.
[0022] Similar considerations apply to reactor/contactor (K) through which is introduced lift steam through line (J) and hot regenerated catalyst through slide valve (Q) and feed through line (HH) and the products and catalyst again empty into preseparator (E) and then into (F) in the same manner as has been previously described with respect to regenerator (B). It is noted that it is also essential that there be an equalizer line (M) from the catalyst stripper (D) back to the cyclones (E) and (F) in the identical same manner as there is between regenerator inventory surge hopper (C) and regenerator (B). Therefore line (M) in the drawing perforns the same function as line (L).
[0023] Typically, the operating parameters for regenerator (B) will be between 1100°F. and 2000'F. and for FCC operations less than 1400°F. The velocity must be greater than 3-1/2 ft. per second in order to assure a dilute phase operation and less than 100 ft. per second and usually will be maintained in the range of 5-15 ft. per second. The pressure on the regenerator will typically be between 5 and 50 psig, preferably between 10 and 30 psig and gas time will typically be between 3 and 15 seconds.
[0024] The reactor system design is very similar to that of the regenerator in the figure in that it also consists of a two separator system (E) and (F) and a stripper (D) which also functions as a surge hopper as well as a riser/contactor (K). The regenerated catalyst is taken from the regenerator surge hopper (C) through valve (Q) into the riser contactor (K). It can be contacted with a diluent such as lift gas, steam, hydrocarbon recycle, or water, or be fed through line (J). There are also provisions (HH) for an optional feed point to control the tine in the contactor or reactor. The regenerated catalyst plus any diluent plus any recycle plus feed is contacted in contactor/reactor (K) for a period of time necessary to obtain the desired yield as either an FCC, heavy oil type FCC, fluid coker or as in an ART (selective vaporization) process, such as that disclosed in U. S. 4,263,128. Again, all of the catalyst as well as all of the vapors produced in reactor/contactor (K) enter into preseparator (E). As in like nanner with regenerator (B), the catalyst and vapors to preseparator (E) are controlled so that the system is not overloaded. The efficiencies of separators (E) and (F) are as discussed on the regenerator system and again the catalyst separated from the vapors is returned through lines (R) below the dense bed level to spent catalyst stripper (D). The spent catalyst stripper (D) is fluidized with steam to the stripper. The vent line (M) fron stripper (D) enters between the separators (E) and (F). Since the amount of entrained material will be quite low, it could Just as easily enter into the inlet to (E) as in the regenerator.
[0025] The spent catalyst then leaves the catalyst strlpper on level control through valve (JJ). The vapors now essentially free of catalyst leave the system through line (H) to fractionation and to separation. In the case of an ART unit they could be quenched at this point. In the case of a fluid coker, FCC or heavy oil FCC, the vapors would go into the fractionation systen and way or may not be quenched.
[0026] From the above description it should be noted that one of the main differences between the systen set forth in the accompanying figure and the aysten of the prior art is that none of the vapors from regeneration system (B) or the contactor (K) are in equilibrium or contact with the catalyst dense bed that would be contained in vessels (C) or (D). Most systems up to this point have a feature where the vapors are separated in the vessel and are in constant contact with the dense bed.
[0027] The contactor (K) conditions are basically between 10 and 100 ft. per second and preferably running at an outlet velocity of about 70 ft. per second. The time depends on whether there is an ART unit; as an ART unit, the time would be preferably less than a second, and normally less than 3 seconds, or as an FCC, which normally operates between 1 second and 5 seconds vapor time. The temperature in the contactor would range between 800 and 1000°F.
[0028] The preseparator (E) is not narrowly critical and all that is required is that there by a very rapid disengagement of circulating solids and vapors. Materials of this type are disclosed in U.S. 4,285,706; U. S. 4,348,215; and U.S. 4,398,932, the entire disclosures of which are herein incorparated by reference. The high efficiency cyclone (F) is a conventional type cyclone as to be understood that it can be one or a plurality of cyclones. Preferred separation (F) is of the multicyclone type, described in U. S. 4,285,706; the disclosure of which is incorporated herein.
[0029] Figure 1 also depicts systems for controlling an FCCU, heavy oil FCCU or ART Process to increase C/O by: directly cooling the circulating catalyst by using a cooler (V) and slide valve (W); lowering the carbon on the circulating material (catalyst or catalytically inert contact material in the case of an ART unit) which in turn will increase the C/0 ratio by lowering the regenerator temperature by reheating the material in the reactor/contactor stripper. This is accomplished by combining hot regenerated material directly to the stripper through slide valve (S) and heating riser (U). Lift media (T) can be either gas or steam. Not only does this result in lower carbon on spent naterial by vaporizing more of the hydrocarbon from the material in the stripper, it has a secondary beneficial effect of superheating the CX/RX vapors which will reduce coke formation through condensation reactions. Since the CX/RX vapors in heavy oil FCC or an ART unit may be at their dew point, any cooling results in condensation of the heavy ends which results in coke formation in the vessel, cyclones and vapor line. This superheating of the vapors will elininate this problem. As shown in the figure an alternative line (Ul) can also be used to superheat the CX/RX vapors and increase the stripper temperature by injecting hot regenerated material and lift media (T) into the outlet of preseparator (E).
[0030] Another feature shown in the figure is using lift gas (J) to lift the regenerated catalyst before contact with the feed (HH) which is injected higher in the riser to control tite in the contactor on reactor riser. This lift gas is used to fort coke on the acid sites before feed addition to reduce coke formation and improve yield structure. In conventional catalyst systems the acid site activity greatly increases as the catalyst is regenerated to carbon levels less than 0.3. This increased acid site .. activity increases coke formation of the hydrocarbon feedstock and reduces selectivity. Therefore, by contacting the catalyst with gas before feed injection the acid sites are deactiviated by carbon formation from the gas and the zeolitic sites, which are selective, are available for cracking the gas oil. This results in increased octane, olefins, and higher C/O.
[0031] Still another feature shown in the figure is the option of putting the hydrocarbon feed directly into the base of the riser at (J) along with lift gas or steam and contacting it with hot regenerated catalyst before contacting it with cooled catalyst for increased C/0 over a heat balanced operation without cooling. This method of operation is beneficial when feeds containing asphaltenes, basic nitrogen and metals are being processed in an FCC system. Using this method allows the operator to first preheat the feed with a minimum of hot regenerated material to remove the majority of the asphaltenes, basic nitrogen and netals so that the cooled catalyst injected just downstrean of the first hot catalyst maintains a high selectivity because the active sites are not covered by asphaltene (coke) deposits, neutralized by basic nitrogen, or competed with by fresh matals activity.
[0032] One skilled in the art of fluidized solid handling would quickly realize the potential of the illustrated transport system to reduce capital costs associated with the installation of this equipment as well as its potential to increase (double) the capacity of existing FCC, heavy oil FCC, fluid coker or ART process units using the existing vessels without major modifications since this system eliminates superficial velocity constraints now in existence with dense bed type regenerators. Also, this fluidized apparatus design concept is applicable to other fluidizable solids systems which have heretofore been limited by superficial bed velocities.
[0033] It is understood that the particular fluidized solid or solids obviously depends on the particular process being carried out.
[0034] Typical solids for cracking include those which have pore structures into which molecules of feed naterial may enter for adsorption and/or for contact with active catalytic sites within or adjacent to the pores. Various types of catalysts are available within this classification, including for example the layered silicates, e.g. smectites. Although the most widely available catalysts within this classification are the well-known zeolite-containing catalysts, non-zeolite catalysts are also contemplated.
[0035] The preferred zeolite-containing catalysts may include any zeolite, whether natural, semi-synthetic or synthetic, alone or in admixture with other materials which do not significantly impair the suitability of the catalyst, provided the resultant catalyst has the activity and pore structure referred to above. For example, if the virgin catalyst is a mixture, it may include the zeolite component associated with or dispersed in a porous refractory inorganic oxide carrier, in such case the catalyst may for example contain about 1% to about 60% more preferably about 15 to about 50%, and most typically about 20 to 45% by weight, based on the total weight of catalyst (water free basis) of the zeolite, the balance of the catalyst being the porous refractory inorganic oxide alone or in combination with any of the known adjuvants for promoting or suppressing various desired and undesired reactions. For a general explanation of the genus of zeolite, molecular sieve catalysts useful in the invention; attention is drawn to the disclosures of the articles entitled "Refinery Catalysts Are a Fluid Business" and "Making Cat Crackers Work on Varied Diet", appearing respectively in the July 26, 1978 and September 13, 1978 issues of Chemical Week magazine. The descriptions of the aforementioned publications are incorporated herein by reference.
[0036] For the most part, the zeolite components of the zeolite- containing catalysts will be those which are known to be useful in FCC cracking processes. In general, these are crystalline aluminosilicates, typically made up of tetra coordinated aluminum atoms associated through oxygen atoms with adjacent silicon atoms in the crystal structure. However, the term "zeolite" as used in this disclosure contemplates not only aluninosilicates, but also substances in which the aluminum has been partly or wholly replaced, such as for instance by gallium, phosphorus, boron, iron, and/or other metal atoms, and further includes substances in which all or part of the silicon has been replaced; such as for instance by gertainiun or phosphorus, titanium and zirconium substitution may also be practiced.
[0037] Most zeolites are prepared or occur naturally in the sodium form, so that sodium cations are associated with the electronegative sites in the crystal structure. The sodium cations tend to make zeolites inactive and much less stable when exposed to hydrocarbon conversion conditions, particularly high tempertures. Accordingly, the zeolite may be ion exchanged, and where the zeolite is a component of a catalyst composition, such ion exchanging may occur before or after incorporation of the zeolite as a component of the composition. Suitable cations for replacement of sodium in the zeolite crystal structure include ammonium (decomposable to hydrogen), hydrogen, rare earth metals, alkaline earth metals, etc. Various suitable ion exchange procedures and cations which may be exchanged into the zeolite crystal structure are well known to those skilled in the art.
[0038] Examples of the naturally occurring crystalline aluminosilicate zeolites which may be used as or included in the catalyst for the present invention are faujasite, mordenite, clinoptilote, chabazite, analcity, crionite, as well as levynite, dachiardite, paulingite, noselite, ferriorite, heulandite, scolccite, stibite, harmotome, phillipsite, brewsterite, flarite, datiolite, gmelinite, caumnite, leucite, lazurite, scaplite, mesolite, ptolite, nephline, matrolite, offretite and sodalite.
[0039] Examples of the synthetic crystalline aluminosilicate zeolites which are useful as or in the catalyst for carrying out the present invention are Zeolite X, U. S. 2,882,244; Zeolite Y, U. S. 3,130,007; and Zeolite A, U. S. Patent No. 2,882,243; as well as Zeolite B, U. S. Patent No. 3,008,803; Zeolite D, Canada Patent No. 661,981; Zeolite E, Canada Patent No. 614,495; Zeolite F, U. S. Patent No. 2,996,358; Zeolite H, U. S. Patent No. 3,010,789; Zeolite J, U. S. Patent No. 3,011,869; Zeolite L, Belgian Patent No. 575,177; Zeolite M, U. S. Patent No. 2,995,423; Zeolite 0, U. S. Patent No. 3,140,252; Zeolite Q, U. S. Patent. No. 2,991,151; Zeolite S, U. S. Patent No. 3,054,657; Zeolite T, U. S. Patent No. 2,950,952; Zeolite W, U. S. Patent No. 3,012,853; Zeolite Z, Canada Patent No. 614,495; and Zeolite Omega, Canada Patent No. 817,915.
[0040] Also ZK-4HJ. alpha beta and ZSM-type zeolites are useful. Moreover, the zeolites described in U. S. Patent Nos. 3,140,249; 3,140,253; 3.944,482; and 4,137,151 are also useful, the disclosures of said patents being incorporated herein by reference.
[0041] The crystalline aluminosilicate zeolites having a faujasite-type crystal structure are particularly preferred for use in the present invention. This includes particularly natural faujasite and Zeolite X and Zeolite Y.
[0043] It is to be emphasized that whilst the invention is described and illustrated above mainly in terms of a cracking process in which the contact material is a cracking catalyst and the riser is a reactor, it applies similarly to a selective vaporisation process in which the contact material is substantially inert catalytically and the riser is termed a contactor. Whether the contact material is catalytic or inert, it does tend to become spent in the riser and is regenerated for recycling by combustion of deposits in the regeneration zone;: terms such as "regeneration zone", "regenerator" etc. are appropriate for both FCC and selective vaporisation systems, though herein terms such as "combustion zone", "combuster" etc. are sometimes used Instead in connection with the selective vaporisation system.
[0044] The invention can thus be seen to provide, inter alia, a process wherein lower boiling products are obtained from a hydrocarbon feed by contacting the feed with fluidized solid contact material at elevated temperature in a riser, spent contact material is separated and stripped of volatile hydrocarbons in a stripping zone, stripped contact material is regenerated with oxygen-containing gas in a regeneration zone, and hot freshly regenerated fluidized solid contact material is returned to the riser, the process further including charging a portion of hot freshly regeneratred fluidized solid material to the stripping zone. This can result in increasing the amount of volatile hydrocarbon stripped in said stripping zone and superheating vapor in said stripping zone, whereby stripped material regenerated in the regenerating zone has a lower carbon content and regenerator temperature can be reduced. Preferably regenerator temperature is reduced and the ratio of fluid solid contact material to oil ratio is increased. Preferably coke formation in cyclones, stripper zone or both is reduced.
GLOSSARY FOR FIGURE
[0045]
A. Air Blower Discharge - Air to Regenerator System
B. Regenerator/Burner/Kiln
C. Regenerator/Surge Hopper
D. Spent Catalyst/ARTCAT Stripper
E. Preseparator
F. High Efficiency Cyclone
G. Flue Gas to Stack/Treating
H. Oil Vapors to Separation
I. Steam to Stripper
J. Lift Stean/Gas (Wet or Dry)/H20 to Riser Contactor or Feed
K. Riser Contactor
L. Surge Hopper Vent
M. Stripper Vent
N. Catalyst Cooler/ARTCAT Cooler
0. Hot Recirculating Material Slide Valve
P. Cold Recirculating Material Slide Valve
Q. Regenerated Material Slide Valve
R. Separated Material from Separators
JJ. Spent Slide Valve
HH. Feed - Optional Feed Point to Control Tine in Contactor
S. Hot Material to Cx/Rx Heating Riser Slide Valve
T. Lift Gas/Stean to Cx/Rx Heating Riser
V. C/0 Control Cooler
W. Cooled Catalyst to Riser Contactor
U. Cx/Rx Stripper Reheat Line
Ul. Cx/Rx Vapor Superheat Line
1. A process wherein lower boiling products are obtained from a hydrocarbon feed by
contacting the feed with fluidized solid contact material at elevated temperature
in a riser, spent contact material is separated and stripped of volatile hydrocarbons
in a stripping zone, stripped contact material is regenerated with oxygen-containing
gas in a regeneration zone, and hot freshly regenerated fluidized solid contact material
is returned to the riser, the process further including charging a portion of hot
freshly regenerated fluidized solid material to the stripping zone.
2. A process according to claim I wherein the contact material is a cracking catalyst
comprising zeolite containing acid sites.
3. A process according to claim 1 wherein the contact material is substantially catalytically
inert and vaporizes volatile hydrocarbons by contact at elevated temperature and unvaporized
portions of the hydrocarbon feed including metals are deposited thereon.
4. A process according to any preceding claim in which the contacting is carried out
in a dilute phase and all of the solid material from the riser is subjected to cyclone
pre-separation with rapid disengagement of solids and gases, the separated solids
being returned to a dense bed a vessel other than the riser.
5. A process according to any preceding claim in which the regeneration is carried
out in a dilute phase and all of the solid material from the regeneration zone is
subjected to cyclone pre-separation with rapid disengagement of solids and gases,
the separated solids being returned to a dense bed in a vessel other than the regeneration
zone.
6. A process according to claim 1 and substantially as hereinbefore described with
reference to the accompanying drawing.